1. Field of the Invention
The present invention relates to a power source device, and more specifically, to a power source device suitable for an image formation apparatus such as a copy machine, printer and the like.
2. Related Background Art
Conventionally, a copy machine and printer include various kinds of independent electric components such as a sequence controller circuit with a microprocessor as a central component thereof for controlling a print sequence as a whole, DC power source, power source for exposure, high voltage power source for charging, and the like, and thus the electric components have a limit in miniaturization and cost reduction.
In particular, since high voltage power supplies are arranged in many cases such that the voltage thereof is lowered once by a DC power source and increased again by a transformer, they employ a plurality of transformers which are disadvantageous in cost, volume and weight in electric components and further have a low power efficiency.
To cope with this problem, there is a proposal to employ a transformer having a plurality of low voltage outputs and high voltage outputs to cover almost all the necessary voltage outputs by a single transformer, wherein the primary of the transformer is usually controlled by detecting a particular output of the secondary thereof and other power source outputs are controlled on the secondary by connecting any control means to a next stage.
FIGS. 8A to 8C show an output voltage detection circuit provided with the secondary of a prior art. In the case shown in FIG. 8A, an output from a diode D2 is simply divided to provide an output voltage detection signal r. In the case shown in FIG. 8B, a detection winding N2-1 is provided and an output therefrom is rectified and smoothed by a diode D3 and capacitor C3 and divided by resistors R1 and R2 to provide an output voltage detection signal r. In the case shown in FIG. 8C, an output from a winding N which is similar to a particular output is rectified and smoothed by a diode D3 and capacitor C3 and divided by resistors R1 and R2 to provide an output voltage detection signal r.
Nevertheless, when a system covering a plurality of voltage outputs by a single converter transformer is employed in the prior art, the circuit shown in FIGS. 8A to 8C are used for detecting a particular output of the secondary.
When control is carried out by the same output as in FIG. 8A, a problem arises in that since a capacitor C2 has a large capacity, an output from the diode 2 has a very slow response and the response of a system as a whole using a signal obtained by dividing an output voltage as the output voltage detection signal r has a slow response with the result that a power source system cannot catch up with a load fluctuation and a ripple is increased, whereas when the rippled is reduced, the system is made unstable.
Further, when the detection winding N2-1 is independently provided as in FIG. 8B and an output voltage detection signal proportional to a particular output is used, a problem arises in that a balance between an output from a winding N and an output from the winding N2-1 causes an error, and further since a current flowing through a diode D2 is changed by a change of load although a response characteristic can be relatively freely set by the resistors R1 and R2 and capacitor C3, a particular output voltage is changed by the V.sub.F /I.sub.F characteristic of the diode D2.
When two rectifying/smoothing paths are provided for an output from a converter transformer as in FIG. 8C and a detection system with a time constant sufficiently shorter than that of an output as a power source is provided, a problem arises in that the DC voltage level of a particular voltage output system may be different from that of a sensing system due to a change of the V.sub.F of the diode D2 caused by a change of load.